why not a 2 man debate like lincoln-douglas?
http://www.nps.gov/liho/learn/historyculture/debates.htm
...Lincoln and Douglas agreed to debate in seven of the nine Illinois Congressional Districts; the seven where Douglas had not already spoken.
In each debate either Douglas or Lincoln would open with an hour address. The other would then speak for an hour and a half. The first then had 30 minutes of rebuttal.
In the seven debates, Douglas, as the incumbent, was allowed to go first four times...